Black matrix in liquid crystal display and method of fabricating the same

ABSTRACT

A liquid crystal display includes a substrate, a gate line on the substrate, a gate insulating layer on the gate line, a data line on the gate insulating layer, a thin film transistor having a gate electrode, a source electrode, and a drain electrode, wherein the gate electrode is connected to the gate line and the source electrode is connected to the data line, a first passivation layer having a first contact hole exposing the drain electrode and covering the data line and the thin film transistor, the first passivation layer having a first resistance, an insulating layer having a second resistance lower than the first resistance and covering the data line and the thin film transistor, a second passivation layer having a second contact hole connected to the first contact hole and on the insulating layer and the first passivation layer, and a pixel electrode on the second passivation layer and contacting the drain electrode through the first and second contact holes.

This application claims the benefit of Korean Application No.P2000-83762, filed on Dec. 28, 2000, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and moreparticularly, to a black matrix in a liquid crystal display and a methodof fabricating the same. Although the present invention is suitable fora wide scope of applications, it is particularly suitable for improvingan aperture ratio.

2. Discussion of the Related Art

Until recently, a cathode-ray tube (CRT) has been mainly developed andused for display devices. However, flat panel displays draw attentionbecause of their small depth dimensions, desirably low weight, and lowvoltage power supply requirements. Presently, thin filmtransistor-liquid crystal displays (TFT-LCDs) with high resolution andsmall depth dimension have been developed.

FIG. 1 shows a conventional liquid crystal display (LCD).

In FIG. 1, the LCD includes upper and lower substrates 5 and 22. A blackmatrix 6, a color filter 7 including sub-color filters (red, green,blue) 8, and a transparent common electrode 18 disposed above the colorfilter 7 are formed on the upper substrate 5. A pixel region “P”, apixel electrode 17 disposed at the pixel region “P”, and an array lineincluding a switching device “T” are formed on the lower substrate 22. Aliquid crystal layer 14 is interposed between the upper and lowersubstrates 5 and 22. The black matrix 6 is formed by deposition andpatterning of an opaque metallic material having a low reflectance or bycoating and patterning an opaque photosensitive resin.

The lower substrate 22 may also be referred to as an array substratewhere thin film transistors “T” are arranged in a matrix configuration,and gate and data lines 13 and 15 that cross the thin film transistors“T” are formed. The pixel region “P” is defined by the gate and datalines 13 and 15, and a transparent conductive metal such asindium-tin-oxide (ITO) having a relatively high transmittance is used asthe pixel electrode 17 on the pixel region “P”.

If a voltage is applied to the common electrode 18 of the uppersubstrate 5 and the pixel electrode 17 of the lower substrate 22, atransmittance of the LCD is changed according to the alignment state ofthe liquid crystal layer 14 so that images can be displayed.

At the lower substrate 22, the data line 15 and the pixel electrode 17is spaced apart from each other, thereby eliminating an electricinterference. Accordingly, the liquid crystal layer on a separatedregion 19 between the data line 15 and the pixel electrode 17 has atransmittance different from the liquid crystal layer on the pixelelectrode 17. Accordingly, a light leakage occurs at the separatedregion 19. To prevent this phenomenon, the black matrix 6 is disposed atthe corresponding region of the upper substrate 5. In the conventionalart, a black matrix is disposed on the upper substrate 5. Thus, theblack matrix is designed to include an alignment margin considering amisalignment in attachment.

However, in the conventional structure of the black matrix, an apertureratio is reduced due to the alignment margin.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a black matrix in aliquid crystal display and a method of fabricating the same thatsubstantially obviates one or more of problems due to limitations anddisadvantages of the related art.

Another object of the present invention is to improve an aperture ratioof an LCD.

Another object of the present invention is to reduce a parasiticcapacitance of an LCD.

Additional features and advantages of the invention will be set forth inthe description which follows and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a liquidcrystal display includes a substrate, a gate line on the substrate, agate insulating layer on the gate line, a data line on the gateinsulating layer, a thin film transistor having a gate electrode, asource electrode, and a drain electrode, wherein the gate electrode isconnected to the gate line and the source electrode is connected to thedata line, a first passivation layer having a first contact holeexposing the drain electrode and covering the data line and the thinfilm transistor, the first passivation layer having a first resistance,an insulating layer having a second resistance lower than the firstresistance and covering the data line and the thin film transistor, asecond passivation layer having a second contact hole connected to thefirst contact hole and on the insulating layer and the first passivationlayer, and a pixel electrode on the second passivation layer andcontacting the drain electrode through the first and second contactholes.

In another aspect of the present invention, a method of fabricating aliquid crystal display includes forming a gate line on a substrate,forming a gate insulating layer on the gate line, forming a data line onthe gate insulating layer, forming a thin film transistor having a gateelectrode, a source electrode, and a drain electrode, forming a firstpassivation layer having a first resistance and covering the data lineand the thin film transistor, forming an insulating layer having asecond resistance lower than the first resistance and covering the dataline and the thin film transistor, forming a second passivation layer onthe insulating layer and the first passivation layer, forming first andsecond contact holes in the first and second passivation layers,respectively, the first contact hole exposing the drain electrode andthe second contact hole connected to the first contact hole, and forminga pixel electrode contacting the drain electrode through the first andsecond contact holes.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a schematic perspective view of a conventional liquid crystaldisplay;

FIG. 2 is a schematic plane view partially showing a lower substrate ofa liquid crystal display according to first and second embodiments ofthe present invention;

FIGS. 3A to 3C are schematic cross-sectional views illustrating afabricating process, taken along the line “III—III” of FIG. 2 accordingto the first embodiment of the present invention; and

FIGS. 4A to 4C are schematic cross-sectional views illustrating afabricating process, taken along the line “III—III” of FIG. 2 accordingto the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIG. 2 is a schematic plane view partially showing a lower substrate ofa liquid crystal display according to first and second embodiments ofthe present invention.

In FIG. 2, gate and data lines 113 and 115 cross each other in the shapeof matrix and a TFT “T” is disposed adjacent to the cross region. TheTFT “T” includes a gate electrode 125, an active layer 119 and sourceand drain electrodes 121 and 123. A pixel electrode 117 is disposed atthe region defined by the intersection of the gate and data lines 113and 115 and connected to the drain electrode 123 through a contact hole127. In addition to the above structure, a black matrix 126 of aninsulating layer is formed on the gate and data lines 113 and 115 andthe TFT “T”, and extended to a separated region “K” between the gateline 113 and the pixel electrode 117 or between the data line 115 andthe pixel electrode 117. Since the separated region “K”, where a lightleakage occurs, is screened by the black matrix 126 of the same lowersubstrate, an aperture ratio of the LCD according to the firstembodiment of the present invention is higher than that of theconventional LCD fabricated considering an alignment margin.

FIGS. 3A to 3C are schematic cross-sectional views illustrating afabricating process, taken along the line “III—III” of FIG. 2.

In FIG. 3A, a gate line 113 (shown in FIG. 2) and a gate electrode 125are formed on a substrate 100 by depositing and patterning a first metallayer. One of conductive metals, such as aluminum (Al), aluminum alloy,copper (Cu), tungsten (W), molybdenum (Mo), and chromium (Cr), is usedfor the first metal layer. Then, a gate insulating layer 130 of siliconnitride (SiNx) or silicon oxide (SiO₂) is formed on the entire substrate100 having the gate electrode 125 thereon. Subsequently, an active layer119 of intrinsic amorphous silicon (a-Si:H) and an ohmic contact layer120 of impurity-doped amorphous silicon (n+ a-Si:H) are formed on thegate insulating layer 130.

In FIG. 3B, a data line 115 crossing the gate line 113 (shown in FIG.2), a source electrode 121 elongated from the data line 115 and a drainelectrode 123 spaced apart from the source electrode 121 are formed onthe ohmic contact layer 120 by depositing and patterning a second metallayer. Then, a first passivation layer 132 of SiNx or SiO₂ having afirst resistance is formed on the entire substrate 100 having the sourceand drain electrodes 121 and 123. The first passivation layer 132prevents the active layer 119 from contacting a black matrix of aninsulating layer 134 having a second resistance lower than the firstresistance. In the absence of the first passivation layer 132, athreshold voltage (V_(th)) of the active layer 119 that contacts theinsulating layer 134 having the second resistance fluctuates so thatover-current or under-current phenomenon may occur when a voltage isapplied to the gate electrode 125. Subsequently, the black matrix isformed on the TFT “T” and the data line 115 by depositing and patterningthe insulating layer 134 such as a color resin or an organic blackmatrix (black resin) having the second resistance lower than the firstresistance. In the case of using the color resin, a color filter may beformed at the pixel region of the lower substrate.

In FIG. 3C, a second passivation layer 136 is formed on the insulatinglayer 134 by depositing an organic insulating layer such as acrylicresin, benzocyclobutene (BCB) or cyclo-olefin resin. Then, first andsecond contact holes 127 and 128 partially exposing the drain electrode123 are formed in the first and second passivation layers 132 and 136,respectively, and a pixel electrode 117 is formed on the secondpassivation layer 136 by depositing and patterning a transparentconductive metal.

Since the LCD according to the first embodiment of the present inventiondoes not need an additional black matrix for an alignment margin, anaperture ratio is improved.

However, since the second resistance of the insulating layer is lowerthan the first resistance of the first passivation layer, a parasiticcapacitance may be generated between the insulating layer 134 and thelower metal line such as data line 115, so that a display quality may bedecreased. To improve this problem, a second embodiment is suggested.

FIGS. 4A to 4C are schematic cross-sectional views illustrating afabricating process, taken along the line “III—III” of FIG. 2 accordingto the second embodiment of the present invention. (Since a plane viewof the LCD according to the second embodiment is the same as the planeview of the LCD according to the first embodiment. Thus, FIG. 2 and itsexplanation can be applied to the second embodiment.)

In FIG. 4A, a gate line (shown as 113 in FIG. 2) and a gate electrode125 are formed on a substrate 100 by depositing and patterning a firstmetal layer. One of conductive metals, such as aluminum (Al), aluminumalloy, copper (Cu), tungsten (W), molybdenum (Mo), and chromium (Cr), isused for the first metal layer. Then, a gate insulating layer 130 ofsilicon nitride (SiNx) or silicon oxide (SiO₂) is formed on the entiresubstrate 100 having the gate electrode 125. Subsequently, an activelayer 119 of intrinsic amorphous silicon (a-Si:H) and an ohmic contactlayer 120 of impurity-doped amorphous silicon (n+ a-Si:H) are formed onthe gate insulating layer 130.

In FIG. 4B, a data line 115 crossing the gate line 113, a sourceelectrode 121 elongated from the data line 115 and a drain electrode 123spaced apart from the source electrode 121 are formed on the ohmiccontact layer 120 by depositing and patterning a second metal layer.Then, a first passivation layer 132 having a first resistance is formedon the TFT “T” and the data line 115 only by depositing and patterningone of SiNx and SiO₂. Hence, the source electrode 121 and one side ofthe data line 115 are exposed at the regions “K1” and “K2”,respectively. Subsequently, a black matrix is formed on the data line115 and the TFT “T” by depositing and patterning an insulating layer 134such as a color resin or an organic black matrix (black resin) having asecond resistance lower than the first resistance. In the case of usingthe color resin, a color filter can be formed at the pixel region of thelower substrate instead of the upper substrate. The insulating layer 134covers the data line 115 including the first passivation layer 132 andis connected to the exposed source electrode 121 at the region “K1” andthe data line 115 at the region “K2”. Therefore, since the insulatinglayer 134 and the data line 115 are connected and equi-potential, aparasitic capacitance is prevented and a display quality is improved.

In FIG. 4C, a second passivation layer 136 is formed on the insulatinglayer 134 by depositing an organic insulating layer such as acrylicresin, benzocyclobutene (BCB) or cyclo-olefin resin. Then, first andsecond contact holes 127 and 128 partially exposing the drain electrode123 are formed in the first and second passivation layers 132 and 136,respectively. A pixel electrode 117 is formed on the second passivationlayer 136 by depositing and patterning a transparent conductive metal.

Consequently, the LCD according to the present invention has someadvantages. First, since the black matrix of the insulating layer isformed on the lower substrate, an aperture ratio is improved byeliminating a necessity of the alignment margin. Second, since theinsulating layer having the second resistance lower than the firstresistance is connected to the lower metal line such as the data line,the parasitic capacitance between the insulating layer and the lowermetal line is not generated. As a result, a degradation in the displayquality due to a cross-talk or a flicker may be prevented.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the black matrix in theliquid crystal display device and the method of fabricating the same ofthe present invention without departing from the spirit or scope of theinventions. Thus, it is intended that the present invention covers themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A liquid crystal display, comprising: asubstrate; a gate line on the substrate; a gate insulating layer on thegate line; a data line on the gate insulating layer; a thin filmtransistor having a gate electrode, a source electrode and a drainelectrode wherein the gate electrode is connected to the gate line andthe source electrode is connected to the data line; a first passivationlayer having a first contact hole exposing the drain electrode andcovering the data line and the thin film transistor, the firstpassivation layer having a first resistance; an insulating layer havinga second resistance lower than the first resistance to contact and coverthe data line and the thin film transistor; a second passivation layerhaving a second contact hole connected to the first contact hole and onthe insulating layer and the first passivation layer; and a pixelelectrode on the second passivation layer and contacting the drainelectrode through the first and second contact holes.
 2. The liquidcrystal display according to claim 1, further comprising a color filteron the first passivation layer.
 3. The liquid crystal display accordingto claim 1, wherein the insulating layer includes one of a color resinand a black resin.
 4. The liquid crystal display according to claim 1,wherein the insulating layer contacts the source electrode and the dataline.
 5. The liquid crystal display according to claim 1, wherein thegate and data lines are selected from the group consisting of aluminum,aluminum alloy, copper, tungsten, molybdenum, and chromium.
 6. Theliquid crystal display according to claim 1, wherein the first andsecond passivation layers include one of a non-organic insulatingmaterial and an organic insulating material.
 7. The liquid crystaldisplay according to claim 1, wherein the pixel electrode includes oneof indium-tin-oxide and indium-zinc-oxide.
 8. The liquid crystal displayaccording to claim 1, wherein the source electrode has a portiondirectly contacting the insulating layer.
 9. The liquid crystal displayaccording to claim 1, wherein the data line has a portion directlycontacting the insulating layer.
 10. A method of fabricating a liquidcrystal display, comprising: forming a gate line on a substrate; forminga gate insulating layer on the gate line; forming a data line on thegate insulating layer; forming a thin film transistor having a gateelectrode, a source electrode, and a drain electrode; forming a firstpassivation layer having a first resistance and covering the data lineand the thin film transistor; forming an insulating layer having asecond resistance lower than the first resistance to cover and contactthe data line and the thin film transistor; forming a second passivationlayer on the insulating layer and the first passivation layer; formingfirst and second contact holes in the first and second passivationlayers, respectively, the first contact hole exposing the drainelectrode and the second contact hole connected to the first contacthole; and forming a pixel electrode contacting the drain electrodethrough the first and second contact holes.
 11. The method according toclaim 10, wherein the insulating layer directly contacts the sourceelectrode and the data line.
 12. The method according to claim 10,further comprising forming a color filter on the first passivationlayer.
 13. The liquid crystal display according to claim 4, wherein theinsulating layer contacts side portions of both the source electrode andthe data line.
 14. The liquid crystal display according to claim 8,wherein the source electrode has a side portion directly contacting theinsulating layer.
 15. The liquid crystal display according to claim 9,wherein the data line has a side portion directly contacting theinsulating layer.
 16. The method according to claim 11, wherein theinsulating layer directly contacts side portions of both the sourceelectrode and the data line.
 17. A liquid crystal display, comprising: asubstrate; a gate line on the substrate; a gate insulating layer on thegate line; a data line on the gate insulating layer; a thin filmtransistor having a gate electrode, a source electrode and a drainelectrode wherein the gate electrode is connected to the gate line andthe source electrode is connected to the data line; a first passivationlayer having a first contact hole exposing the drain electrode andcovering the data line and the thin film transistor, the firstpassivation layer having a first resistance; an insulating layer havinga second resistance lower than the first resistance and covering thedata line and the thin film transistor; a second passivation layerhaving a second contact hole connected to the first contact hole and onthe insulating layer and the first passivation layer; and a pixelelectrode on the second passivation layer and contacting the drainelectrode through the first and second contact holes, wherein theinsulating layer contacts the source electrode and the data line.
 18. Aliquid crystal display, comprising: a substrate; a gate line on thesubstrate; a gate insulating layer on the gate line; a data line on thegate insulating layer; a thin film transistor having a gate electrode, asource electrode and a drain electrode wherein the gate electrode isconnected to the gate line and the source electrode is connected to thedata line; a first passivation layer having a first contact holeexposing the drain electrode and covering the data line and the thinfilm transistor, the first passivation layer having a first resistance;an insulating layer having a second resistance lower than the firstresistance and covering the data line and the thin film transistor; asecond passivation layer having a second contact hole connected to thefirst contact hole and on the insulating layer and the first passivationlayer; and a pixel electrode on the second passivation layer andcontacting the drain electrode through the first and second contactholes, wherein the source electrode has a portion directly contactingthe insulating layer.
 19. A liquid crystal display, comprising: asubstrate; a gate line on the substrate; a gate insulating layer on thegate line; a data line on the gate insulating layer; a thin filmtransistor having a gate electrode, a source electrode and a drainelectrode wherein the gate electrode is connected to the gate line andthe source electrode is connected to the data line; a first passivationlayer having a first contact hole exposing the drain electrode andcovering the data line and the thin film transistor, the firstpassivation layer having a first resistance; an insulating layer havinga second resistance lower than the first resistance and covering thedata line and the thin film transistor; a second passivation layerhaving a second contact hole connected to the first contact hole and onthe insulating layer and the first passivation layer; and a pixelelectrode on the second passivation layer and contacting the drainelectrode through the first and second contact holes, wherein the dataline has a portion directly contacting the insulating layer.
 20. Amethod of fabricating a liquid crystal display, comprising: forming agate line on a substrate; forming a gate insulating layer on the gateline; forming a data line on the gate insulating layer; forming a thinfilm transistor having a gate electrode, a source electrode, and a drainelectrode; forming a first passivation layer having a first resistanceand covering the data line and the thin film transistor; forming aninsulating layer having a second resistance lower than the firstresistance and covering the data line and the thin film transistor;forming a second passivation layer on the insulating layer and the firstpassivation layer; forming first and second contact holes in the firstand second passivation layers, respectively, the first contact holeexposing the drain electrode and the second contact hole connected tothe first contact hole; and forming a pixel electrode contacting thedrain electrode through the first and second contact holes, wherein theinsulating layer directly contacts the source electrode and the dataline.